<?php
/** @file
 * CSS selector parsing classes.
 *
 * This file contains the tools necessary for parsing CSS 3 selectors.
 * In the future it may be expanded to handle all of CSS 3.
 *
 * The parser contained herein is has an event-based API. Implementors should
 * begin by implementing the {@link CssEventHandler} interface. For an example
 * of how this is done, see {@link CssEventHandler.php}.
 *
 * @author M Butcher <matt@aleph-null.tv>
 * @license http://opensource.org/licenses/lgpl-2.1.php The GNU Lesser GPL (LGPL) or an MIT-like license. 
 */

/** @addtogroup querypath_css CSS Parsing
 * QueryPath includes a CSS 3 Selector parser.
 *
 *
 * Typically the parser is not accessed directly. Most developers will use it indirectly from
 * qp(), htmlqp(), or one of the methods on a QueryPath object.
 *
 * This parser is modular and is not tied to QueryPath, so you can use it in your 
 * own (non-QueryPath) projects if you wish. To dive in, start with CssEventHandler, the
 * event interface that works like a SAX API for CSS selectors. If you want to check out
 * the details, check out the parser (CssParser),  scanner (CssScanner), and token list (CssToken).
 */

require_once 'CssEventHandler.php';


/**
 * An event handler for handling CSS 3 Selector parsing.
 *
 * This provides a standard interface for CSS 3 Selector event handling. As the 
 * parser parses a selector, it will fire events. Implementations of CssEventHandler
 * can then handle the events.
 *
 * This library is inspired by the SAX2 API for parsing XML. Each component of a 
 * selector fires an event, passing the necessary data on to the event handler.
 *
 * @ingroup querypath_css
 */
interface CssEventHandler
{
    /** The is-exactly (=) operator. */
    const isExactly = 0; // =
    /** The contains-with-space operator (~=). */
    const containsWithSpace = 1; // ~=
    /** The contains-with-hyphen operator (!=). */
    const containsWithHyphen = 2; // |=
    /** The contains-in-string operator (*=). */
    const containsInString = 3; // *=
    /** The begins-with operator (^=). */
    const beginsWith = 4; // ^=
    /** The ends-with operator ($=). */
    const endsWith = 5; // $=
    /** The any-element operator (*). */
    const anyElement = '*';

    /**
     * This event is fired when a CSS ID is encountered.
     * An ID begins with an octothorp: #name.
     *
     * @param string $id
     *  The ID passed in.
     */
    public function elementID($id); // #name

    /**
     * Handle an element name.
     * Example: name
     * @param string $name
     *  The name of the element.
     */
    public function element($name); // name

    /**
     * Handle a namespaced element name.
     * example: namespace|name
     * @param string $name
     *  The tag name.
     * @param string $namespace
     *  The namespace identifier (Not the URI)
     */
    public function elementNS($name, $namespace = NULL);

    /**
     * Handle an any-element (*) operator.
     * Example: *
     */
    public function anyElement(); // *

    /**
     * Handle an any-element operator that is constrained to a namespace.
     * Example: ns|*
     * @param string $ns
     *  The namespace identifier (not the URI).
     */
    public function anyElementInNS($ns); // ns|*

    /**
     * Handle a CSS class selector.
     * Example: .name
     * @param string $name
     *  The name of the class.
     */
    public function elementClass($name); // .name

    /**
     * Handle an attribute selector.
     * Example: [name=attr]
     * Example: [name~=attr]
     * @param string $name
     *  The attribute name.
     * @param string $value
     *  The value of the attribute, if given.
     * @param int $operation
     *  The operation to be used for matching. See {@link CssEventHandler}
     *  constants for a list of supported operations.
     */
    public function attribute($name, $value = NULL, $operation = CssEventHandler::isExactly); // [name=attr]

    /**
     * Handle an attribute selector bound to a specific namespace.
     * Example: [ns|name=attr]
     * Example: [ns|name~=attr]
     * @param string $name
     *  The attribute name.
     * @param string $ns
     *  The namespace identifier (not the URI).
     * @param string $value
     *  The value of the attribute, if given.
     * @param int $operation
     *  The operation to be used for matching. See {@link CssEventHandler}
     *  constants for a list of supported operations.
     */
    public function attributeNS($name, $ns, $value = NULL, $operation = CssEventHandler::isExactly);

    /**
     * Handle a pseudo-class.
     * Example: :name(value)
     * @param string $name
     *  The pseudo-class name.
     * @param string $value
     *  The value, if one is found.
     */
    public function pseudoClass($name, $value = NULL); //:name(value)

    /**
     * Handle a pseudo-element.
     * Example: ::name
     * @param string $name
     *  The pseudo-element name.
     */
    public function pseudoElement($name); // ::name

    /**
     * Handle a direct descendant combinator.
     * Example: >
     */
    public function directDescendant(); // >

    /**
     * Handle a adjacent combinator.
     * Example: +
     */
    public function adjacent(); // +

    /**
     * Handle an another-selector combinator.
     * Example: ,
     */
    public function anotherSelector(); // ,

    /**
     * Handle a sibling combinator.
     * Example: ~
     */
    public function sibling(); // ~ combinator

    /**
     * Handle an any-descendant combinator.
     * Example: ' '
     */
    public function anyDescendant(); // ' ' (space) operator.
  
}

/**
 * Tokens for CSS.
 * This class defines the recognized tokens for the parser, and also 
 * provides utility functions for error reporting.
 *
 * @ingroup querypath_css
 */
final class CssToken
{
    const char = 0;
    const star = 1;
    const rangle = 2;
    const dot = 3;
    const octo = 4;
    const rsquare = 5;
    const lsquare = 6;
    const colon = 7;
    const rparen = 8;
    const lparen = 9;
    const plus = 10;
    const tilde = 11;
    const eq = 12;
    const pipe = 13;
    const comma = 14;
    const white = 15;
    const quote = 16;
    const squote = 17;
    const bslash = 18;
    const carat = 19;
    const dollar = 20;
    const at = 21; // This is not in the spec. Apparently, old broken CSS uses it.

    // In legal range for string.
    const stringLegal = 99;

    /**
     * Get a name for a given constant. Used for error handling.
     */
    static function name($const_int)
    {
        $a = array('character', 'star', 'right angle bracket',
            'dot', 'octothorp', 'right square bracket', 'left square bracket',
            'colon', 'right parenthesis', 'left parenthesis', 'plus', 'tilde',
            'equals', 'vertical bar', 'comma', 'space', 'quote', 'single quote',
            'backslash', 'carat', 'dollar', 'at');
        if (isset($a[$const_int]) && is_numeric($const_int)) {
            return $a[$const_int];
    } elseif ($const_int == 99) {
            return 'a legal non-alphanumeric character';
        } elseif ($const_int == FALSE) {
            return 'end of file';
        }
        return sprintf('illegal character (%s)', $const_int);
    }
}

/**
 * Parse a CSS selector.
 *
 * In CSS, a selector is used to identify which element or elements
 * in a DOM are being selected for the application of a particular style.
 * Effectively, selectors function as a query language for a structured
 * document -- almost always HTML or XML.
 *
 * This class provides an event-based parser for CSS selectors. It can be
 * used, for example, as a basis for writing a DOM query engine based on
 * CSS.
 *
 * @ingroup querypath_css
 */
class CssParser
{
    protected $scanner = NULL;
    protected $buffer = '';
    protected $handler = NULL;
    protected $strict = FALSE;

    protected $DEBUG = FALSE;

    /**
     * Construct a new CSS parser object. This will attempt to
     * parse the string as a CSS selector. As it parses, it will
     * send events to the CssEventHandler implementation.
     */
    public function __construct($string, CssEventHandler $handler)
    {
        $this->originalString = $string;
        $is = new CssInputStream($string);
        $this->scanner = new CssScanner($is);
        $this->handler = $handler;
    }

    /**
     * Parse the selector.
     *
     * This begins an event-based parsing process that will
     * fire events as the selector is handled. A CssEventHandler
     * implementation will be responsible for handling the events.
     * @throws CssParseException
     */
    public function parse()
    {

        $this->scanner->nextToken();
        while ($this->scanner->token !== FALSE) {
            // Primitive recursion detection.
            $position = $this->scanner->position();

            if ($this->DEBUG) {
                print "PARSE " . $this->scanner->token . "\n";
            }
            $this->selector();

            $finalPosition = $this->scanner->position();

            if ($this->scanner->token !== FALSE && $finalPosition == $position) {
                // If we get here, then the scanner did not pop a single character
                // off of the input stream during a full run of the parser, which
                // means that the current input does not match any recognizable
                // pattern.
                throw new CssParseException('CSS selector is not well formed.');
            }
      
    }

    }

    /**
     * A restricted parser that can only parse simple selectors.
     * The pseudoClass handler for this parser will throw an
     * exception if it encounters a pseudo-element or the
     * negation pseudo-class.
     *
     * @deprecated This is not used anywhere in QueryPath and
     *  may be removed.
     *//*
  public function parseSimpleSelector() {
    while ($this->scanner->token !== FALSE) {
      if ($this->DEBUG) print "SIMPLE SELECTOR\n";
      $this->allElements();
      $this->elementName();
      $this->elementClass();
      $this->elementID();
      $this->pseudoClass(TRUE); // Operate in restricted mode.
      $this->attribute();
      
      // TODO: Need to add failure conditions here.
    }
  }*/

    /**
     * Handle an entire CSS selector.
     */
    private function selector()
    {
        if ($this->DEBUG) print "SELECTOR{$this->scanner->position()}\n";
        $this->consumeWhitespace(); // Remove leading whitespace
        $this->simpleSelectors();
        $this->combinator();
    }

    /**
     * Consume whitespace and return a count of the number of whitespace consumed.
     */
    private function consumeWhitespace()
    {
        if ($this->DEBUG) print "CONSUME WHITESPACE\n";
        $white = 0;
        while ($this->scanner->token == CssToken::white) {
            $this->scanner->nextToken();
            ++$white;
    }
        return $white;
    }

    /**
     * Handle one of the five combinators: '>', '+', ' ', '~', and ','.
     * This will call the appropriate event handlers.
     * @see CssEventHandler::directDescendant(),
     * @see CssEventHandler::adjacent(),
     * @see CssEventHandler::anyDescendant(),
     * @see CssEventHandler::anotherSelector().
     */
    private function combinator()
    {
        if ($this->DEBUG) print "COMBINATOR\n";
        /*
         * Problem: ' ' and ' > ' are both valid combinators.
         * So we have to track whitespace consumption to see
         * if we are hitting the ' ' combinator or if the
         * selector just has whitespace padding another combinator.
         */

        // Flag to indicate that post-checks need doing
        $inCombinator = FALSE;
        $white = $this->consumeWhitespace();
        $t = $this->scanner->token;

        if ($t == CssToken::rangle) {
            $this->handler->directDescendant();
            $this->scanner->nextToken();
            $inCombinator = TRUE;
            //$this->simpleSelectors();
    } elseif ($t == CssToken::plus) {
            $this->handler->adjacent();
            $this->scanner->nextToken();
            $inCombinator = TRUE;
            //$this->simpleSelectors();
    } elseif ($t == CssToken::comma) {
            $this->handler->anotherSelector();
            $this->scanner->nextToken();
            $inCombinator = TRUE;
            //$this->scanner->selectors();
    } elseif ($t == CssToken::tilde) {
            $this->handler->sibling();
            $this->scanner->nextToken();
            $inCombinator = TRUE;
    }

        // Check that we don't get two combinators in a row.
        if ($inCombinator) {
            $white = 0;
            if ($this->DEBUG) print "COMBINATOR: " . CssToken::name($t) . "\n";
            $this->consumeWhitespace();
            if ($this->isCombinator($this->scanner->token)) {
                throw new CssParseException("Illegal combinator: Cannot have two combinators in sequence.");
            }
    } // Check to see if we have whitespace combinator:
        elseif ($white > 0) {
            if ($this->DEBUG) print "COMBINATOR: any descendant\n";
            $inCombinator = TRUE;
            $this->handler->anyDescendant();
        } else {
            if ($this->DEBUG) print "COMBINATOR: no combinator found.\n";
        }
    }

    /**
     * Check if the token is a combinator.
     */
    private function isCombinator($tok)
    {
        $combinators = array(CssToken::plus, CssToken::rangle, CssToken::comma, CssToken::tilde);
        return in_array($tok, $combinators);
    }

    /**
     * Handle a simple selector.
     */
    private function simpleSelectors()
    {
        if ($this->DEBUG) print "SIMPLE SELECTOR\n";
        $this->allElements();
        $this->elementName();
        $this->elementClass();
        $this->elementID();
        $this->pseudoClass();
        $this->attribute();
    }

    /**
     * Handles CSS ID selectors.
     * This will call CssEventHandler::elementID().
     */
    private function elementID()
    {
        if ($this->DEBUG) print "ELEMENT ID\n";
        if ($this->scanner->token == CssToken::octo) {
            $this->scanner->nextToken();
            if ($this->scanner->token !== CssToken::char) {
                throw new CssParseException("Expected string after #");
            }
            $id = $this->scanner->getNameString();
            $this->handler->elementID($id);
        }
    }

    /**
     * Handles CSS class selectors.
     * This will call the CssEventHandler::elementClass() method.
     */
    private function elementClass()
    {
        if ($this->DEBUG) print "ELEMENT CLASS\n";
        if ($this->scanner->token == CssToken::dot) {
            $this->scanner->nextToken();
            $this->consumeWhitespace(); // We're very fault tolerent. This should prob through error.
            $cssClass = $this->scanner->getNameString();
            $this->handler->elementClass($cssClass);
        }
    }

    /**
     * Handle a pseudo-class and pseudo-element.
     *
     * CSS 3 selectors support separate pseudo-elements, using :: instead
     * of : for separator. This is now supported, and calls the pseudoElement
     * handler, CssEventHandler::pseudoElement().
     *
     * This will call CssEventHandler::pseudoClass() when a
     * pseudo-class is parsed.
     */
    private function pseudoClass($restricted = FALSE)
    {
        if ($this->DEBUG) print "PSEUDO-CLASS\n";
        if ($this->scanner->token == CssToken::colon) {

            // Check for CSS 3 pseudo element:
            $isPseudoElement = FALSE;
            if ($this->scanner->nextToken() === CssToken::colon) {
                $isPseudoElement = TRUE;
                $this->scanner->nextToken();
            }

            $name = $this->scanner->getNameString();
            if ($restricted && $name == 'not') {
                throw new CssParseException("The 'not' pseudo-class is illegal in this context.");
            }

            $value = NULL;
            if ($this->scanner->token == CssToken::lparen) {
                if ($isPseudoElement) {
                    throw new CssParseException("Illegal left paren. Pseudo-Element cannot have arguments.");
        }
                $value = $this->pseudoClassValue();
            }

            // FIXME: This should throw errors when pseudo element has values.
            if ($isPseudoElement) {
                if ($restricted) {
                    throw new CssParseException("Pseudo-Elements are illegal in this context.");
                }
                $this->handler->pseudoElement($name);
                $this->consumeWhitespace();

                // Per the spec, pseudo-elements must be the last items in a selector, so we
                // check to make sure that we are either at the end of the stream or that a
                // new selector is starting. Only one pseudo-element is allowed per selector.
                if ($this->scanner->token !== FALSE && $this->scanner->token !== CssToken::comma) {
                    throw new CssParseException("A Pseudo-Element must be the last item in a selector.");
                }
            } else {
                $this->handler->pseudoClass($name, $value);
            }
    }
    }

    /**
     * Get the value of a pseudo-classes.
     *
     * @return string
     *  Returns the value found from a pseudo-class.
     *
     * @todo Pseudoclasses can be passed pseudo-elements and
     *  other pseudo-classes as values, which means :pseudo(::pseudo)
     *  is legal.
     */
    private function pseudoClassValue()
    {
        if ($this->scanner->token == CssToken::lparen) {
            $buf = '';

            // For now, just leave pseudoClass value vague.
            /*
            // We have to peek to see if next char is a colon because
            // pseudo-classes and pseudo-elements are legal strings here.
            print $this->scanner->peek();
            if ($this->scanner->peek() == ':') {
              print "Is pseudo\n";
              $this->scanner->nextToken();

              // Pseudo class
              if ($this->scanner->token == CssToken::colon) {
                $buf .= ':';
                $this->scanner->nextToken();
                // Pseudo element
                if ($this->scanner->token == CssToken::colon) {
                  $buf .= ':';
                  $this->scanner->nextToken();
                }
                // Ident
                $buf .= $this->scanner->getNameString();
              }
            }
            else {
              print "fetching string.\n";
              $buf .= $this->scanner->getQuotedString();
              if ($this->scanner->token != CssToken::rparen) {
                $this->throwError(CssToken::rparen, $this->scanner->token);
              }
              $this->scanner->nextToken();
            }
            return $buf;
            */
            $buf .= $this->scanner->getQuotedString();
            return $buf;
    }
    }

    /**
     * Handle element names.
     * This will call the CssEventHandler::elementName().
     *
     * This handles:
     * <code>
     *  name (CssEventHandler::element())
     *  |name (CssEventHandler::element())
     *  ns|name (CssEventHandler::elementNS())
     *  ns|* (CssEventHandler::elementNS())
     * </code>
     */
    private function elementName()
    {
        if ($this->DEBUG) print "ELEMENT NAME\n";
        if ($this->scanner->token === CssToken::pipe) {
            // We have '|name', which is equiv to 'name'
            $this->scanner->nextToken();
            $this->consumeWhitespace();
            $elementName = $this->scanner->getNameString();
            $this->handler->element($elementName);
        } elseif ($this->scanner->token === CssToken::char) {
            $elementName = $this->scanner->getNameString();
            if ($this->scanner->token == CssToken::pipe) {
                // Get ns|name
                $elementNS = $elementName;
                $this->scanner->nextToken();
                $this->consumeWhitespace();
                if ($this->scanner->token === CssToken::star) {
                    // We have ns|*
                    $this->handler->anyElementInNS($elementNS);
                    $this->scanner->nextToken();
        } elseif ($this->scanner->token !== CssToken::char) {
                    $this->throwError(CssToken::char, $this->scanner->token);
                } else {
                    $elementName = $this->scanner->getNameString();
                    // We have ns|name
                    $this->handler->elementNS($elementName, $elementNS);
                }

            } else {
                $this->handler->element($elementName);
            }
    }
    }

    /**
     * Check for all elements designators. Due to the new CSS 3 namespace
     * support, this is slightly more complicated, now, as it handles
     * the *|name and *|* cases as well as *.
     *
     * Calls CssEventHandler::anyElement() or CssEventHandler::elementName().
     */
    private function allElements()
    {
        if ($this->scanner->token === CssToken::star) {
            $this->scanner->nextToken();
            if ($this->scanner->token === CssToken::pipe) {
                $this->scanner->nextToken();
        if ($this->scanner->token === CssToken::star) {
            // We got *|*. According to spec, this requires
            // that the element has a namespace, so we pass it on
            // to the handler:
            $this->scanner->nextToken();
            $this->handler->anyElementInNS('*');
        } else {
            // We got *|name, which means the name MUST be in a namespce,
            // so we pass this off to elementNameNS().
            $name = $this->scanner->getNameString();
            $this->handler->elementNS($name, '*');
        }
            } else {
                $this->handler->anyElement();
            }
    }
    }

    /**
     * Handler an attribute.
     * An attribute can be in one of two forms:
     * <code>[attrName]</code>
     * or
     * <code>[attrName="AttrValue"]</code>
     *
     * This may call the following event handlers: CssEventHandler::attribute().
     */
    private function attribute()
    {
        if ($this->scanner->token == CssToken::lsquare) {
            $attrVal = $op = $ns = NULL;

            $this->scanner->nextToken();
            $this->consumeWhitespace();

            if ($this->scanner->token === CssToken::at) {
                if ($this->strict) {
                    throw new CssParseException('The @ is illegal in attributes.');
                } else {
                    $this->scanner->nextToken();
                    $this->consumeWhitespace();
                }
            }

            if ($this->scanner->token === CssToken::star) {
                // Global namespace... requires that attr be prefixed,
                // so we pass this on to a namespace handler.
                $ns = '*';
                $this->scanner->nextToken();
            }
            if ($this->scanner->token === CssToken::pipe) {
                // Skip this. It's a global namespace.
                $this->scanner->nextToken();
                $this->consumeWhitespace();
            }

            $attrName = $this->scanner->getNameString();
            $this->consumeWhitespace();

            // Check for namespace attribute: ns|attr. We have to peek() to make
            // sure that we haven't hit the |= operator, which looks the same.
            if ($this->scanner->token === CssToken::pipe && $this->scanner->peek() !== '=') {
                // We have a namespaced attribute.
                $ns = $attrName;
                $this->scanner->nextToken();
                $attrName = $this->scanner->getNameString();
                $this->consumeWhitespace();
            }

            // Note: We require that operators do not have spaces
            // between characters, e.g. ~= , not ~ =.

            // Get the operator:
            switch ($this->scanner->token) {
                case CssToken::eq:
                    $this->consumeWhitespace();
                    $op = CssEventHandler::isExactly;
                    break;
                case CssToken::tilde:
                    if ($this->scanner->nextToken() !== CssToken::eq) {
                        $this->throwError(CssToken::eq, $this->scanner->token);
                    }
                    $op = CssEventHandler::containsWithSpace;
                    break;
                case CssToken::pipe:
                    if ($this->scanner->nextToken() !== CssToken::eq) {
                        $this->throwError(CssToken::eq, $this->scanner->token);
                    }
                    $op = CssEventHandler::containsWithHyphen;
                    break;
                case CssToken::star:
                    if ($this->scanner->nextToken() !== CssToken::eq) {
                        $this->throwError(CssToken::eq, $this->scanner->token);
                    }
                    $op = CssEventHandler::containsInString;
                    break;
                case CssToken::dollar;
                    if ($this->scanner->nextToken() !== CssToken::eq) {
                        $this->throwError(CssToken::eq, $this->scanner->token);
                    }
                    $op = CssEventHandler::endsWith;
                    break;
                case CssToken::carat:
                    if ($this->scanner->nextToken() !== CssToken::eq) {
                        $this->throwError(CssToken::eq, $this->scanner->token);
                    }
                    $op = CssEventHandler::beginsWith;
                    break;
            }

            if (isset($op)) {
                // Consume '=' and go on.
                $this->scanner->nextToken();
                $this->consumeWhitespace();

                // So... here we have a problem. The grammer suggests that the
                // value here is String1 or String2, both of which are enclosed
                // in quotes of some sort, and both of which allow lots of special
                // characters. But the spec itself includes examples like this:
                //   [lang=fr]
                // So some bareword support is assumed. To get around this, we assume
                // that bare words follow the NAME rules, while quoted strings follow
                // the String1/String2 rules.

                if ($this->scanner->token === CssToken::quote || $this->scanner->token === CssToken::squote) {
                    $attrVal = $this->scanner->getQuotedString();
        } else {
                    $attrVal = $this->scanner->getNameString();
                }

                if ($this->DEBUG) {
                    print "ATTR: $attrVal AND OP: $op\n";
                }
            }

            $this->consumeWhitespace();

            if ($this->scanner->token != CssToken::rsquare) {
                $this->throwError(CssToken::rsquare, $this->scanner->token);
            }

            if (isset($ns)) {
                $this->handler->attributeNS($attrName, $ns, $attrVal, $op);
            } elseif (isset($attrVal)) {
                $this->handler->attribute($attrName, $attrVal, $op);
            } else {
                $this->handler->attribute($attrName);
            }
            $this->scanner->nextToken();
    }
    }

    /**
     * Utility for throwing a consistantly-formatted parse error.
     */
    private function throwError($expected, $got)
    {
        $filter = sprintf('Expected %s, got %s', CssToken::name($expected), CssToken::name($got));
        throw new CssParseException($filter);
    }
  
}

/**
 * Scanner for CSS selector parsing.
 *
 * This provides a simple scanner for traversing an input stream.
 *
 * @ingroup querypath_css
 */
final class CssScanner
{
    var $is = NULL;
    public $value = NULL;
    public $token = NULL;

    var $recurse = FALSE;
    var $it = 0;

    /**
     * Given a new input stream, tokenize the CSS selector string.
     * @see CssInputStream
     * @param CssInputStream $in
     *  An input stream to be scanned.
     */
    public function __construct(CssInputStream $in)
    {
        $this->is = $in;
    }

    /**
     * Return the position of the reader in the string.
     */
    public function position()
    {
        return $this->is->position;
    }

    /**
     * See the next char without removing it from the stack.
     *
     * @return char
     *  Returns the next character on the stack.
     */
    public function peek()
    {
        return $this->is->peek();
    }

    /**
     * Get the next token in the input stream.
     *
     * This sets the current token to the value of the next token in
     * the stream.
     *
     * @return int
     *  Returns an int value corresponding to one of the CssToken constants,
     *  or FALSE if the end of the string is reached. (Remember to use
     *  strong equality checking on FALSE, since 0 is a valid token id.)
     */
    public function nextToken()
    {
        $tok = -1;
        ++$this->it;
        if ($this->is->isEmpty()) {
            if ($this->recurse) {
                throw new Exception("Recursion error detected at iteration " . $this->it . '.');
                exit();
            }
            //print "{$this->it}: All done\n";
            $this->recurse = TRUE;
            $this->token = FALSE;
            return FALSE;
    }
        $ch = $this->is->consume();
        //print __FUNCTION__ . " Testing $ch.\n";
        if (ctype_space($ch)) {
            $this->value = ' '; // Collapse all WS to a space.
            $this->token = $tok = CssToken::white;
            //$ch = $this->is->consume();
            return $tok;
    }

        if (ctype_alnum($ch) || $ch == '-' || $ch == '_') {
            // It's a character
            $this->value = $ch; //strtolower($ch);
            $this->token = $tok = CssToken::char;
            return $tok;
    }

        $this->value = $ch;

        switch ($ch) {
            case '*':
                $tok = CssToken::star;
                break;
            case chr(ord('>')):
                $tok = CssToken::rangle;
                break;
            case '.':
                $tok = CssToken::dot;
                break;
            case '#':
                $tok = CssToken::octo;
                break;
            case '[':
                $tok = CssToken::lsquare;
                break;
            case ']':
                $tok = CssToken::rsquare;
                break;
            case ':':
                $tok = CssToken::colon;
                break;
            case '(':
                $tok = CssToken::lparen;
                break;
            case ')':
                $tok = CssToken::rparen;
                break;
            case '+':
                $tok = CssToken::plus;
                break;
            case '~':
                $tok = CssToken::tilde;
                break;
            case '=':
                $tok = CssToken::eq;
                break;
            case '|':
                $tok = CssToken::pipe;
                break;
            case ',':
                $tok = CssToken::comma;
                break;
            case chr(34):
                $tok = CssToken::quote;
                break;
            case "'":
                $tok = CssToken::squote;
                break;
            case '\\':
                $tok = CssToken::bslash;
                break;
            case '^':
                $tok = CssToken::carat;
                break;
            case '$':
                $tok = CssToken::dollar;
                break;
            case '@':
                $tok = CssToken::at;
                break;
        }


        // Catch all characters that are legal within strings.
        if ($tok == -1) {
            // TODO: This should be UTF-8 compatible, but PHP doesn't
            // have a native UTF-8 string. Should we use external
            // mbstring library?

            $ord = ord($ch);
            // Characters in this pool are legal for use inside of
            // certain strings. Extended ASCII is used here, though I
            // Don't know if these are really legal.
            if (($ord >= 32 && $ord <= 126) || ($ord >= 128 && $ord <= 255)) {
                $tok = CssToken::stringLegal;
            } else {
                throw new CSSParseException('Illegal character found in stream: ' . $ord);
            }
        }

        $this->token = $tok;
        return $tok;
    }

    /**
     * Get a name string from the input stream.
     * A name string must be composed of
     * only characters defined in CssToken:char: -_a-zA-Z0-9
     */
    public function getNameString()
    {
        $buf = '';
        while ($this->token === CssToken::char) {
            $buf .= $this->value;
            $this->nextToken();
            //print '_';
        }
        return $buf;
    }

    /**
     * This gets a string with any legal 'string' characters.
     * See CSS Selectors specification, section 11, for the
     * definition of string.
     *
     * This will check for string1, string2, and the case where a
     * string is unquoted (Oddly absent from the "official" grammar,
     * though such strings are present as examples in the spec.)
     *
     * Note:
     * Though the grammar supplied by CSS 3 Selectors section 11 does not
     * address the contents of a pseudo-class value, the spec itself indicates
     * that a pseudo-class value is a "value between parenthesis" [6.6]. The
     * examples given use URLs among other things, making them closer to the
     * definition of 'string' than to 'name'. So we handle them here as strings.
     */
    public function getQuotedString()
    {
        if ($this->token == CssToken::quote || $this->token == CssToken::squote || $this->token == CssToken::lparen) {
            $end = ($this->token == CssToken::lparen) ? CssToken::rparen : $this->token;
            $buf = '';
            $escape = FALSE;

            $this->nextToken(); // Skip the opening quote/paren

            // The second conjunct is probably not necessary.
            while ($this->token !== FALSE && $this->token > -1) {
                //print "Char: $this->value \n";
                if ($this->token == CssToken::bslash && !$escape) {
                    // XXX: The backslash (\) is removed here.
                    // Turn on escaping.
                    //$buf .= $this->value;
                    $escape = TRUE;
        } elseif ($escape) {
                    // Turn off escaping
                    $buf .= $this->value;
                    $escape = FALSE;
        } elseif ($this->token === $end) {
                    // At end of string; skip token and break.
                    $this->nextToken();
                    break;
        } else {
                    // Append char.
                    $buf .= $this->value;
        }
                $this->nextToken();
            }
            return $buf;
    }
    }

    /**
     * Get a string from the input stream.
     * This is a convenience function for getting a string of
     * characters that are either alphanumber or whitespace. See
     * the CssToken::white and CssToken::char definitions.
     *
     * @deprecated This is not used anywhere in QueryPath.
     *//*
  public function getStringPlusWhitespace() {
    $buf = '';
    if($this->token === FALSE) {return '';}
    while ($this->token === CssToken::char || $this->token == CssToken::white) {
      $buf .= $this->value;
      $this->nextToken();
    }
    return $buf;
  }*/

}

/**
 * Simple wrapper to turn a string into an input stream.
 * This provides a standard interface on top of an array of 
 * characters.
 */
class CssInputStream
{
    protected $stream = NULL;
    public $position = 0;

    /**
     * Build a new CSS input stream from a string.
     *
     * @param string
     *  String to turn into an input stream.
     */
    function __construct($string)
    {
        $this->stream = str_split($string);
    }

    /**
     * Look ahead one character.
     *
     * @return char
     *  Returns the next character, but does not remove it from
     *  the stream.
     */
    function peek()
    {
        return $this->stream[0];
    }

    /**
     * Get the next unconsumed character in the stream.
     * This will remove that character from the front of the
     * stream and return it.
     */
    function consume()
    {
        $ret = array_shift($this->stream);
        if (!empty($ret)) {
            $this->position++;
    }
        return $ret;
    }

    /**
     * Check if the stream is empty.
     * @return boolean
     *   Returns TRUE when the stream is empty, FALSE otherwise.
     */
    function isEmpty()
    {
        return count($this->stream) == 0;
    }
}

/**
 * Exception indicating an error in CSS parsing.
 *
 * @ingroup querypath_css
 */
class CSSParseException extends EXCEPTION
{
}